BTW what do you think about lifepo4 battery for energy storage? I was doing some goggle on that topic and that chemistry type was popping out quite often...
Since you asked - IMHO, LFP serves quite a niche purpose. It's best for replacing 12V lead acid system, as it's the only li-ion chemistry that happens to have compatible voltage range so that a 4s pack can almost directly replace a 12V lead pack. For other li-ion chemistries, 3½ cells would be required
. The voltage curve is more flat, too. It's really close to lead acid. It's case-by-case whether it needs
some tweak in the product voltage setpoints, or
some management, but chances are it is completely a drop-in, even without a BMS, and people do that anyway.
LFP was a really biggie 15 years ago, academically, and for small battery startups, which picked it up for manufacturability reasons AFAIK. Possibly some patent reasons as well, I'm not sure.
LFP was touted as the next big thing. Back then, the only commercial li-ion chemistry was LCO (originally commercialized by Sony), with energy density around 160Wh/kg back then. LFP was supposedly 130Wh/kg, a fair compromise, with supposedly radically lower manufacturing costs (due to abundance of iron and phoshpor, compared to the price of cobalt!); and supposedly radically better safety.
Safety-wise, the thermal runaway onset temperature of LFP is somewhere well over 300 degC (IIRC) compared to the frightening ~150 degC of LCO, and even then, the thermal energy release in the runaway is more benign. But, this ends up as a fallacy; the batteries are complete products, and the safety is the sum of all chemical and physical design within the cell. Even with the imminent danger of the LCO cathode material, the bare cathode chemistry is just one thing. LFP cathode is still not completely safe, and can run away thermally, producing nasty amount of energy release. The electrolyte is still the same, flammable liquid, which shoots burning out of the cell due to the internal pressure, because no one has come up with a better non-flammable electrolyte.
And then, it comes to R&D and engineering:
Because the LCO, and upcoming LMO, NCA, NMC, were more marketable with their higher energy density, they received the actual R&D budget, going through safety improvements, such as advanced shutdown separators (meaning the plastic or ceramic layer in the cell melts "shut" and works as an insulator, stopping the ion transfer, in overheating parts of the cell), or physical cell design things, such as embedded fuses, current-interrupting rupture valves...
As a result, what do we have now, available on the real market, for putting into real products?
Very few LFP products. I have seen numerous safety tests where A123 and K2 cells failed more dramatically than our contemporary high-energy-density cells. Why? They are made by small players, with limited resources in safety engineering. They believe they have chosen a "safe" chemistry, giving the classical "false sense of security". Or, they are some Chinese players (like the absolute classic Winston Chung) not too interested about the actual safety. Happens in China, not saying there isn't good engineering there as well. And maybe they are right, maybe we are too fixated on safety here?
And, in the end, what do we have? We have:
* LFP cells are
still at around 130Wh/kg (actually many Chinese LFP plastic boxes at below 100Wh/kg), which cost around $300-$400/kWh,
while rest of the world has gone forward, and so,
* the modern NCA/NMC cells are at around 250Wh/kg, and cost around $200-$300/kWh!
Especially for mobile anything, this energy density difference is baffling. It makes a real difference whether an EV can drive for 150km or 300km on a single charge! Or, if you can play your "sponsored by NSA" Candy Crunch whatever app for baffling 2 hours straight instead of just one!
What's left after this, are fairly empty promises that an LFP cell lasts for 2000-3000 full cycles while an NCA cell lasts for only 500 full cycles. The point is moot if the NCA cell can be derated to, say, 70% capacity for the same price (yet much lighter weight), increasing the cycle rating manyfolds, or who cares about a promise of 2000-3000 cycle promise if the manufacturer is either just on the brink of bankrupt, or a Shenzen special? Who knows all the failure modes and aging modes for those cells without extensive testing? I did quite a lot of such testing and found out that:
1) The reason the Samsung NCA cell is "only" specified for 500 cycles is that they actually test them, guarantee them, and add a generous safety margin. They actually tend to last approx. 1000 cycles on their own conditions,
2) Number 1 way to increase cycle life in NCA cells is to reduce charging current near full state-of-charge. That's where the cycling damage occurs. Want to fast charge at 1C? Do it, but taper it off after 4.0V.
We saw the same discussion, only on stereoids, with lithium titanate cells, which is even inferior per energy density and price, but supposedly even better per safety and storage and cycle life. Charge from zero to full in just 10 minutes! OK, true, but... what do you do with this rating, when you can get, with the same money, and with the same weight, and NCA pack which charges
equal amount of energy in the same 10 minutes, but then still has 5 times more capacity left you can still go on charging! Or, who cares with claims of 10000 cycle lifetime, if you need to do 5 times more cycles because of the miniscule capacity of the pack, and after just 5000 cycles, it's already swelling and leaking electrolyte despite manufacturer promises (disclaimer: this last part is industry hearsay, but it's better than internet forum hearsay.)
So yeah, I don't see use for LFP anywhere except 12V replacement, but YMMV, and maybe I'm not 100% correct in all this. I'll change my opinion for energy storage as soon someone starts making LFP cells for considerably lower price (per kWh) than NCA right now. That would require over 50% price drop, however; I'm not holding my breath. OTOH, the market right now is price-fixed by the Chinese manufacturers. Price fixing is not dictated by laws of physics, so it can suddenly stop, given right conditions.
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